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148:, Britain's deepest cave lies under the northern slopes of Carreg Cadno. The vertical interval between the sink of the Byfre Fechan stream at Pwll Byfre and its resurgence at Ffynnon Ddu is 300m / 1000 ft. The
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sand where the gritstone has been intensively weathered. An economically valuable deposit of silica sand was worked near Pwll Byfre for many years and transported by tramroad to make
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has been established to protect both the surface features and the vegetation and habitats which they provide and also the extensive cave network beneath.
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on their polished upper surfaces due to scratching by stones embedded in the base of a moving icesheet during the last
60:. Its summit at OS grid ref SN 874161 reaches a height of 538m / 1763 ft above sea level. The hill is within the
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as the underlying limestone has dissolved away and caverns have collapsed. There are also areas of both
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in both the limestone and the gritstone areas. Substantial areas of gritstone country have
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British
Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' & accompanying memoir
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Ordnance Survey
Explorer map OL12 'Brecon Beacons National Park: western area'
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The hill is designated as open country and so freely available to walkers. A
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images of Carreg Cadno and the surrounding area on the
Geograph website
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83:, a coarse quartzitic sandstone (gritstone), formerly known as the
176:. Many walkers start in a car park beside the limestone quarry at
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for 'rock of the fox'') is a hill five miles northeast of
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crosses the northern flanks of the hill in an east-west arc from
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Carreg Cadno, a rocky outcrop on the moorland east of
Penwyllt
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and gritstone pavement. The latter occasionally retain
99:. The northern slopes are formed from the underlying
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The southern slopes of the hill are formed from the
103:. The area displays various features typical of
138:('firebricks' or 'silica bricks') at the nearby
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67:which is owned and managed by the
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107:landscapes including hundreds of
91:Series, and laid down during the
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69:Countryside Council for Wales
266:Mountains and hills of Powys
54:Brecon Beacons National Park
16:Hill (538m) in Powys, Wales
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142:Dinas Silica Brick Works.
130:There are also pockets of
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180:(OS grid ref SN855156).
150:national nature reserve
127:some 18,000 years ago.
101:Carboniferous Limestone
65:National Nature Reserve
52:. It lies within the
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97:Carboniferous period
58:Fforest Fawr Geopark
238: /
242:51.8300°N 3.6335°W
117:limestone pavement
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136:refractory bricks
44:in the county of
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247:51.8300; -3.6335
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164:followed by the
146:Ogof Ffynnon Ddu
62:Ogof Ffynnon Ddu
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162:public footpath
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81:Twrch Sandstone
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184:External links
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89:Millstone Grit
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95:stage of the
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271:Fforest Fawr
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170:Ystradfellte
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32:Carreg Cadno
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245: /
166:Beacons Way
260:Categories
230:51°49′48″N
196:References
121:striations
109:shakeholes
85:Basal Grit
233:3°38′01″W
113:foundered
178:Penwyllt
174:Penwyllt
140:Penwyllt
93:Namurian
48:, south
42:Abercraf
125:ice age
105:karstic
87:of the
75:Geology
156:Access
132:silica
50:Wales
46:Powys
38:Welsh
56:and
172:to
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